1. Field of the Invention
The invention relates to a high-efficiency method for producing glycols from cellulosic materials, and more particularly to a method for catalytically producing glycols from cellulosic materials with ternary catalysts under hydrothermal conditions.
2. Description of the Related Art
Ethylene glycol and 1,2-propylene glycol are important energy liquid fuels, and also important feedstock for the synthesis of polyesters, such as poly(ethylene terephthalate), poly(ethylene naphthalate) and unsaturated polyester resin. They are also used as antifreeze, lubricant, plasticizer, surfactant and etc., and to be feedstock for organic chemical engineering with wide applications.
Producing glycols with renewable biomass can reduce human dependence on fossil energy resources, and contributes to achieving environmentally benign and sustainable development of economy. Cellulosic biomass, including carbohydrates Cn(H2O)m of cellulose, hemicellulose, crop straw, corn cob, rice stalk, wheat stalk, miscanthus, pine wood, birch wood, and aspen wood etc., are abundant in nature. With the development of agricultural technologies, the productivity of cellulosic biomass is increasing. Producing glycols using cellulosic biomass not only reduces dependence on the petroleum resource to some extent, but also realize further processing of agricultural products for value-added chemicals.
At present, ethylene glycol can be obtained by catalytic hydrogenation of cellulose under hydrothermal conditions (Literature 1: Direct catalytic conversion of cellulose into ethylene glycol using nickel-promoted tungsten carbide catalysts, Angew. Chem. Int. Ed. 2008, 47, 8510-8513; Literature 2: Transition metal-tungsten bimetallic catalysts for the conversion of cellulose into ethylene glycol, ChemSusChem 2010, 3, 63-66: Literature 3; CN 101735014 A, Method for producing ethylene glycol from carbohydrate compounds; Literature 4: CN 102190562 A, Method for producing ethylene glycol from carbohydrate compounds). These methods employ tungsten-based catalysts and hydrogenation catalysts as composite catalysts for cellulose conversion, and obtain the ethylene glycol at yields of 60-75%. Similarly, by using binary catalysts of oxidized-status tungsten and hydrogenation catalysts, cellulose, starch and the compounds containing sugars could be efficiently converted into ethylene glycol and 1,2-propylene glycol under hydrothermal and hydrogenating conditions (Literature 5: Method for producing ethylene glycol from polyhydroxy compounds WO2011113281A).
These processes give high ethylene glycol yield and selectivity. However, under high concentration of feedstock or with different feedstock, the reaction time has to be remarkably prolonged and leads to the low efficiency of reaction; Meanwhile, because partial products readily undergo degradation in the presence of catalysts, and eventually influenced glycols yields.
In this invention, a method is provided to realize direct conversion of cellulosic materials feedstock into glycols, including ethylene glycol and 1,2-propylene glycol, in the presence of ternary catalysts of inorganic or organic acids, transition metals of Groups 8, 9 or 10 and tungsten-based catalysts. This invention is not only readily to operate with low cost, but also significantly increases the efficiency of catalytic transformation of cellulosic feedstock as well as the space time yield of glycols.